<!DOCTYPE html>
<html lang="en">

<head>
    <title>Document</title>
    <style>
        .box {
            /* 居中 */
            margin: 0 auto;
            width: 0px;
            height: 0px;
            border-top: 20px solid rgba(48, 31, 141, 0);
            border-right: 20px solid rgba(29, 114, 117, 1);
            border-bottom: 20px solid rgba(170, 22, 136, 0);
            border-left: 20px solid rgba(144, 175, 29, 1);
        }
    </style>
</head>

<body>
    <div class="box"></div>
</body>

</html>